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  • 1
    ISSN: 1573-4994
    Keywords: Protein fluorescence ; distributional analysis ; AIDS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Fluorescence spectroscopy has been applied to the single tryptophan-containing regulatory protein Rev of human immunodeficiency virus (HIV-1). The fluorescence emission was found to have a maximum at 336 nm which refers to a surrounding of the chromophore of intermediate polarity. Fluorescence transients recorded at the maximum of fluorescence were found to decay nonexponentially. A bimodal lifetime distribution is obtained from exponential series analysis (ESM) with centers at 1.7 and 4.5 ns. Two microenvironments for tryptophan are suggested to be responsible for the two lifetime distributions. No innerfilter effect occurred in a Rev solution up to a concentration of 40 μM. A data quality study of ESM analysis as function of collected counts in the peak channel maximum (CIM) showed that, for reliable reconvolution, at least 15,000 CIM are necessary. The widths of the two distributions are shown to be temperature dependent. The broadening of the lifetime distributions when the temperature is raised to 50°C is interpreted as extension of the number of conformational substates which do not interconvert on the fluorescence time scale. The thermal deactivation (temperature quenching) is reflected in a constant decrease in the center of the short-lived lifetime distribution.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 26 (1998), S. 306-315 
    ISSN: 0142-2421
    Keywords: polycarbonate ; SF6 ; plasma ; XPS, SFM ; AFM ; mass spectroscopy ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A systematic investigation was made of the chemical and morphological influences of SF6 plasma on polycarbonate and the influence of plasma treatment on Al metallization. Mass and ion spectroscopy were used for characterization of the plasma and the etching process. X-ray photoelectron spectroscopy (XPS) measurements were applied for the chemical characterization, while atomic force microscopy (AFM) (static and dynamic mode) served to inspect the surface morphology. All analytical techniques were performed in an ultrahigh vacuum system, in order to prevent the polycarbonate sample from being exposed to ambient air after the plasma treatment. During the etching process we used mass difference spectra to demonstrate the removal of masses 19, 28 and 32 corresponding to HF, CO (N2) and CF. Additionally, the inclusion of fluorine was also observed by this technique.The XPS spectra of polycarbonate surfaces show a significant inclusion of fluorine (C-F, C-F2) and a reduction of the oxygen content after the plasma treatment. Aluminium metallization leads to the formation of an Al-F interlayer; metallic growth of Al is only observed when the metallic layers become thicker than a few nanometres.The AFM investigations have shown that even a short plasma treatment causes changes in morphology (structures with an extension of 20-40 nm). After extended plasma exposure the surface becomes very rough, resulting in poor Al adhesion. On untreated polycarbonate, Al grows in the form of weakly bound clusters, which can only be imaged in the dynamic AFM mode. After plasma treatment, Al grows in the form of well-adhering flat layers without clustering. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
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